Programmable logic controller, CPU unit, function unit, method, and program

ABSTRACT

A temperature detector ( 201 ) of an input unit ( 200 ) acquires a temperature of the input unit ( 200 ). A temperature detector ( 301 ) of an output unit ( 300 ) acquires a temperature of the output unit ( 300 ). When the temperature of the input unit ( 200 ) or the output unit ( 300 ) satisfies a preset condition, an input/output manager ( 101 ) of the CPU unit ( 100 ) controls passage/blockage of a signal from the detector ( 901 ) to the input unit ( 200 ) or a signal from the output unit ( 300 ) to a control target device ( 902 ) in accordance with preset content of signal input/output restriction.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on PCT filing PCT/JP2018/031008, filedAug. 22, 2018, the entire contents of which are incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates to a programmable logic controller, a CPUunit, a function unit, a method, and a program.

BACKGROUND ART

A programmable logic controller includes a plurality of units includinga central processing unit (CPU) unit that performs an operation using aninput signal from a detection device and outputs an output signal forcontrol of a device to be controlled, an input unit that inputs to theCPU unit the input signal from the detection device, an output unit thatoutputs the output signal of the CPU unit to the device to becontrolled, and the like.

An input signal circuit of the input unit detects a signal, indicatingON/OFF, received from the detection device. However, a temperature of aninput element increases due to factors including frequent turning-on ofthe input element and a prolonged ON period of the input element. As aresult, a temperature in the input unit becomes high, which may causemalfunction of operation of the input unit or failure of an electronicpart in the input unit.

An output signal circuit of the output unit outputs a signal indicatingON/OFF for a control target device. However, a temperature of an outputelement increases due to factors such as frequent turning-on of theoutput element and a prolonged ON period of the output element. As aresult, a temperature in the output element becomes high, which maycause malfunction of operation of the output unit or failure of anelectronic part inside the output unit.

To avoid such circumstances, Patent Literature 1 mentions determinationof an average of ratios of input/output points that turn onsimultaneously relative to a total number of input/output points, andnotification of an abnormality when the average exceeds a thresholdindicating an allowable ON state.

CITATION LIST Patent Literature

Patent Literature 1: Unexamined Japanese Patent Application PublicationNo. 2013-205878

SUMMARY OF INVENTION Technical Problem

In the configuration disclosed in Patent Literature 1, notification ofoccurrence of the abnormality is made when an internal temperatureincreases, but the programmable logic controller continuously operateseven while making the abnormality notification. Thus, for example, delayin the time when a user notices the abnormality notification may causebreakdown of the unit, which may greatly affect operations of aproduction line, a control system, and the like.

Moreover, conventionally the supply of power to the input unit and theoutput unit is limited in accordance with the temperature in the unit.However, in a case where the power supplied to the input unit and theoutput unit is limited and the input unit and the output unit areoperated at power less than a rated value, a malfunction is assumed tooccur. For example, the input unit may supply to the CPU unit an inputsignal unconverted to a necessary signal level due to limitation of thesupplied power. In this case, the CPU unit is assumed not to be able toproperly identify an input value from the supplied input signal. Inaddition, the output unit cannot convert the output signal to anecessary signal level, and the output device supplied with the outputsignal is assumed not to operate normally.

Here, devices to be controlled by the programmable logic controller mayinclude a device for which input/output restriction is not desirable.For example, restriction of an input indicating that an emergency stopbutton is pushed is undesirable from a safety hazard perspective. Anormal operation in such an input/output case is to be guaranteed.

In view of the above circumstances, an objective of the presentdisclosure is to prevent failure due to rise in temperature of a unitwhile guaranteeing an input/output related operation that is not to berestricted.

Solution to Problem

To achieve the above objective, a programmable logic controller of thepresent disclosure includes a CPU unit and a function unit that includesat least one of an input function of inputting to the CPU unit a signalsupplied from an external device or an output function of outputting tothe external device a signal supplied from the CPU unit. Acquisitionmeans acquires a temperature of the function unit. Control meanscontrols, when the temperature of the function unit satisfies a presetcondition, passage and blockage of the signal from the external deviceto the function unit or the signal from the function unit to theexternal device in accordance with preset content of signal input/outputrestriction.

Advantageous Effects of Invention

The programmable logic controller of the present disclosure controls,when the temperature of the function unit satisfies the presetcondition, passage and blockage of the signal from the external deviceor the signal from the function unit to the external device inaccordance with the preset content of the signal input/outputrestriction. Such configuration can prevent failure of the unit withoutstoppage of input and output for an input/output signal that is not tobe restricted.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a hardware configuration of aprogrammable logic controller and an engineering tool according to anembodiment;

FIG. 2 is a block diagram illustrating a functional configuration of theprogrammable logic controller according to the embodiment;

FIG. 3 is a diagram illustrating an example of data registered in arestriction table according to the embodiment;

FIG. 4A is a diagram illustrating a screen showing a configuration ofthe programmable logic controller in the engineering tool according tothe embodiment;

FIG. 4B is a diagram illustrating a selection screen of input/outputpoints in the engineering tool according to the embodiment;

FIG. 4C is a diagram illustrating a setting screen of an operation of aninput/output point in the engineering tool according to the embodiment;

FIG. 5 is a flowchart of a temperature monitoring process ofinput/output units according to the embodiment;

FIG. 6A is a flowchart of an input/output control process of a CPU unitaccording to the embodiment;

FIG. 6B is a flowchart of a setting update process of input and outputunits according to the embodiment;

FIG. 7A is a timing chart of an output signal for describing an exampleof a method for input/output restriction by an input/output manageraccording to Modified Example 1;

FIG. 7B is a timing chart of an output signal for description of anotherexample of a method for input/output restriction by the input/outputmanager according to Modified Example 1;

FIG. 8 is a diagram illustrating an example of data registered in arestriction table according to Modified Example 2;

FIG. 9 is a flowchart of a temperature monitoring process according toModified Example 2;

FIG. 10 is a flowchart of an input/output control process according toModified Example 2; and

FIG. 11 is a flowchart of a restriction control content determinationprocess according to Modified Example 3.

DESCRIPTION OF EMBODIMENTS

A programmable logic controller 1 according to an embodiment of thepresent disclosure is described hereinafter in detail with reference tothe drawings.

Embodiment

As illustrated in FIG. 1, the programmable logic controller 1 includes acentral processing unit (CPU) unit 100 that controls the overallprogrammable logic controller 1, an input unit 200 that inputs to theCPU unit 100 a signal supplied from a detector 901, and an output unit300 that outputs to a control target device 902 a signal supplied fromthe CPU unit 100. The programmable logic controller 1 controls thedetector 901 and the control target device 902 that operate in, forexample, a production system, a control system, or the like. A signalsupplied from the detector 901 to the input unit 200 may be hereinafterreferred to as an input signal. A signal supplied from the CPU unit 100to the output unit 300 may be hereinafter referred to as an outputsignal. The input signal and the output signal may be collectivelyreferred to as input/output signals. The CPU unit 100 is an example ofthe CPU unit of the present disclosure. The input unit 200 and theoutput unit 300 are examples of the function unit of the presentdisclosure. The detector 901 and the control target device 902 areexamples of the external device of the present disclosure.

The programmable logic controller 1 monitors temperatures in units thatare the input unit 200 and the output unit 300 having input/outputfunctions, and performs input/output restriction when a temperature inthe unit exceeds a set threshold. Here, input/output restrictionincludes meanings of blocking input of a signal from the detector 901 tothe input unit 200 and blocking output of a signal from the output unit300 to a non-control target 902. However, the programmable logiccontroller 1 performs control so as not to impose restriction for presetinput/output signals, that is, not to block the signals.

The detector 901 including a sensor, a switch, and the like is connectedto the input unit 200. The input unit 200 converts the input signalreceived from the detector 901 and indicating ON/OFF to a determinedsignal level, and supplies the converted input signal to the CPU unit100.

The CPU unit 100 executes each instruction of a program in accordancewith ON/OFF of the input signal supplied from the input unit 200 toperform a sequence of operations such as series/parallel connection of acontact, and outputs to the output unit 300 as the output signal anoperation result represented by ON/OFF.

The control target device 902 including an actuator, solenoid valve, anindicator lamp, and the like is connected to the output unit 300. Theoutput unit 300 converts, to a determined signal level, the outputsignal received from the CPU unit 100 and indicating ON/OFF, andsupplies the converted output signal to the control target device 902.

For example, the CPU unit 100 supplies to the output unit 300 an ONsignal as an instruction to drive an actuator of the control targetdevice 902 and an OFF signal as an instruction to stop the actuator.

The CPU unit 100, the input unit 200, and the output unit 300 areconnected to an unillustrated power supply unit via a base unit 400 andoperate with power supplied from the power supply unit. The CPU unit100, the input unit 200, and the output unit 300 are also connected viaa shared bus 410 and communicate with one another via the shared bus410.

As illustrated in FIG. 1, the CPU unit 100 includes, as a hardwareconfiguration, a memory 110 that stores various kinds of programs anddata, an input/output interface (I/F) circuit 120 that communicates withthe input unit 200 and the output unit 300, a tool I/F circuit 130 forcommunication with an engineering tool 500 described later, and a CPU140 that controls the whole CPU unit 100. The memory 110, theinput/output I/F circuit 120, the tool I/F circuit 130 are eachconnected via a bus 190 to the CPU 140 and communicate with the CPU 140.

The memory 110 includes a volatile memory and a non-volatile memory, andstores various kinds of programs and parameters necessary for executionof the programs. The memory 110 is used as a working memory of the CPU140.

The input/output I/F circuit 120 converts, to an electrical signal, thedata supplied from the CPU 140, and sends the converted signal via theshared bus 410 to the input unit 200 and the output unit 300. Theinput/output I/F circuit 120 returns to data the electrical signalreceived from the input unit 200 and the output unit 300 and outputs thedata to the CPU 140.

The tool I/F circuit 130 is an interface for the CPU unit 100 tocommunicate with the engineering tool 500 described later.

The CPU 140 is a computing device and executes various kinds of programsstored in the memory 110 to implement various kinds of functions of theCPU unit 100.

The input unit 200 includes, as a hardware configuration, a memory 210that stores various kinds of data, an input/output I/F circuit 220 thatcommunicates with the CPU unit 100, a temperature measurement circuit230 that measures a temperature in the input unit 200, an input circuit240 that receives a signal from the detector 901, and a micro processingunit (MPU) 250 that controls the whole CPU unit 200. The memory 210, theinput/output I/F circuit 220, the temperature measurement circuit 230,and the input circuit 240 are connected via a bus 290 to the MPU 250 andcommunicate with the MPU 250.

The memory 210 includes a volatile memory and a non-volatile memory, andstores various kinds of programs to implement functions of the inputunit 200. The memory 210 includes a shared memory accessible by the CPUunit 100.

The input/output I/F circuit 220 converts, to an electrical signal, thedata supplied from the MPU 250, and returns to data the electricalsignal received from the CPU unit 100 and outputs the data to the MPU250.

The temperature measurement circuit 230 includes one or more temperaturedetection elements disposed in the input unit 200, and measures atemperature in the input unit 200 and outputs the measurement value tothe MPU 250.

The input circuit 240 is connected to an unillustrated input terminal ofthe input unit 200. The input terminal is connected to an unillustratedoutput terminal of the detector 901 via wiring. The input circuit 240converts, to a determined signal level, the input signal supplied fromthe detector 901, and outputs the converted input signal to the MPU 250.The input circuit 240 includes a switching element that switches betweenconduction and shut-off of the electrical signal. When the switchingelement of the input circuit 240 is turned off, the input circuit 240and the input terminal are in a shut-off state. As a result, the inputunit 200 and the detector 901 are not in electrical communication witheach other and a signal is not input from the detector 901 to the inputunit 200. By contrast, when the switching element of the input circuit240 is turned on, the input circuit 240 and the input terminal are in aconducting state. As a result, the input unit 200 and the detector 901are in electrical communication with each other, and a signal is inputfrom the detector 901 to the input unit 200.

The MPU 250 is a computing device and executes various kinds of programsstored in the memory 210 to implement various kinds of functions of theinput unit 200. The MPU 250 sends, to the CPU unit 100 via theinput/output I/F circuit 220, data supplied from the temperaturemeasurement circuit 230 and indicating a temperature in the input unit200. The MPU 250 sends, to the CPU unit 100 via the input/output I/Fcircuit 220, the input signal of the detector 901 supplied from theinput circuit 240.

The output unit 300 includes, as a hardware configuration, a memory 310that stores various kinds of data, an input/output I/F circuit 320 thatcommunicates with the CPU unit 100, a temperature measurement circuit330 that measures a temperature in the output unit 300, an outputcircuit 340 that outputs a control signal to the control target device902, and an MPU 350 that controls the whole output unit 300. The memory310, the input/output I/F circuit 320, the temperature measurementcircuit 330, and the output circuit 340 are each connected via a bus 390to the MPU 350 and communicate with the MPU 350.

The memory 310 includes a volatile memory and a non-volatile memory, andstores a program for implementing a function of the output unit 300. Thememory 310 includes a shared memory accessible by the CPU unit 100.

The input/output I/F circuit 320 converts, to an electrical signal, thedata supplied from the MPU 350 and returns to data the electrical signalreceived from the CPU unit 100 to and output the data to the MPU 350.

The temperature measurement circuit 330 includes one or more temperaturedetection elements disposed in the output unit 300, and measures atemperature in the output unit 300 and outputs the measurement value tothe MPU 350.

The output circuit 340 is connected to an unillustrated output terminalof the output unit 300. The output terminal is connected to anunillustrated input terminal of the control target device 902 viawiring. The output circuit 340 converts, to a determined signal level,the output signal supplied from the MPU 350 and outputs the convertedoutput signal to the control target device 902. The output circuit 340includes a switching element that switches between conduction andshut-off of the electrical signal. When the switching element of theoutput circuit 340 is turned off, the output circuit 340 and the outputterminal are in a shut-off state. As a result, the output unit 300 andthe control target device 902 are not in electrical communication witheach other and a signal is not output from the output unit 300 to thecontrol target device 902. By contrast, when the switching element ofthe output circuit 340 is turned on, the output circuit 340 and theoutput terminal are in a conducting state. As a result, the output unit300 and the control target device 902 are in electrical communicationwith each other, and a signal is output from the output unit 300 to thecontrol target device 902.

The MPU 350 is a computing device and executes various kinds of programsstored in the memory 310 to implement various kinds of functions of theoutput unit 300. The MPU 350 sends, to the CPU unit 100 via theinput/output I/F circuit 320, the data supplied from the temperaturemeasurement circuit 330 and indicating a temperature in the output unit300. The MPU 350 outputs to the output circuit 340 the output signalsupplied from the CPU unit 100 to be sent to the control target device902.

Hereinafter, the input terminal of the input unit 200 to which the inputsignal is input may be referred to as an input point, and the outputterminal of the output unit 300 from which the output signal is outputmay be referred to as an output point. The input point and the outputpoint may be collectively referred to as input/output points.

The engineering tool 500 is a device formed by a personal computer inwhich an application for setting about input/output restriction of theinput unit 200 or the output unit 300 is installed. The engineering tool500 includes a storage 510 that stores various kinds of data, aninputter 520 that detects an input operation of a user, a display 530that displays an image on a display device, a tool interface 540 forcommunication with the CPU unit 100, and a CPU 550 that controls thewhole engineering tool 500. Each part of the engineering tool isconnected to one another via a bus 590.

The storage 510 includes an operating system program 511 and a settingapplication 512. The operating system program 511 is a program forcontrolling the whole engineering tool 500. The setting application 512is a program for setting with respect to input/output restriction of theinput unit 200 and the output unit 300.

In setting of the input/output restriction, the storage 510 stores datarelating to a configuration of the programmable logic controller 1 to beused. This data includes, for example, information specifying each unitincluded in the programmable logic controller 1. The storage 510 alsostores data specifying input/output points of each unit. This dataincludes, for example, information for identifying each input point, forhow many input points the input unit 200 has, and the like.

The inputter 520 includes an input device such as a keyboard and/or amouse, and receives an operation input from a user, and outputs to theCPU 550 a signal based on the received operation. The display 530includes an image display device, and outputs an image on a screen ofthe image display device in accordance with control of the CPU 550.

The tool interface 540 receives and sends data from and to the CPU unit100 connected via a communication cable 501 in accordance with controlof the CPU 550.

The CPU 550 executes the operating system program 511 to activate theoperating system and control the whole engineering tool 500. The CPU 550executes the setting application 512 on the operating system toimplement a function of setting of the input/output restriction.

Next, a functional configuration of the CPU unit 100, the input unit200, and the output unit 300 is described with reference to FIG. 2.

The CPU unit 100 functionally includes an input/output manager 101 thatmanages input/output of each of the input unit 200 and the output unit300, a restriction table 111 that specifies passage/blockage of a signalof each input/output when the input/output of the input unit 200 and theoutput unit 300 is restricted, and a restriction state storage 112 thatstores a value indicating a state of input/output restriction for eachof the input unit 200 and the output unit 300. The input/output manager101 is an example of control means of the present disclosure.

The restriction table 111 stores information indicating whichinput/output point, among the input/output points of the input unit 200and the output unit 300, is restricted when the input/output isrestricted. For the input point for which the restriction table 111specifies that input is restricted, the input unit 200 blocks the inputsignal from the detector 901. For the output point for which therestriction table 111 specifies that output is restricted, the outputunit 300 blocks the output signal to the control target device 902. Asillustrated in FIG. 3, the restriction table 111 stores informationindicating a target unit, information for identification of theinput/output points, and information indicating whether or not theinput/output point is blocked during the input/output restriction. Inthe illustrated example, the term “OFF” means that the input signal orthe output signal is blocked. The term “ON” means that the input signalor the output signal is passed. The data of the restriction table 111 isset by the user. The restriction table 111 is implemented by use of thememory 110. The restriction table 111 is an example of restrictionstorage means of the present disclosure.

In the example illustrated in FIG. 3, the operation at the time ofinput/output restriction is set to “OFF” for the “input point 1001” inthe restriction table 111. This indicates that input of the signal tothe “input point 1001” is blocked at the time of input/outputrestriction. For the “input point 1002”, the operation at the time ofinput/output restriction is set to “ON” for the “input point 1002”. Thisindicates that the input for the “input point 1002” is received even atthe time of input/output restriction.

Upon receipt of a notification that a measured temperature in a unitamong the input unit 200 and the output unit 300 exceeds a setthreshold, the input/output manager 101 notifies that unit to perform aninput/output restriction in accordance with setting content of therestriction table 111. The input/output manager 101 is implemented byuse of the CPU 140.

Values indicating whether each of the input unit 200 and the output unit300 is in a state of input/output restriction or a state of input/outputnon-restriction are set in the restriction state storage 112. In therestriction state storage 112, the value “1” is set as a valueindicating that the input/output is in “restriction” or the value “0” isset as a value indicating that the input/output is in “non-restriction”for each of the input unit 200 and the output unit 300. The restrictionstate storage 112 is implemented by use of the memory 110.

The input unit 200 functionally includes a temperature detector 201 thatdetects a temperature in the unit, an input controller 202 that controlsinput from the detector 901, a threshold storage 211 that stores athreshold of a temperature that is a reference as to whether or not aninput restriction is performed, an input setting 212 that stores contentfor setting passage/blockage of a signal in each input point, and arestriction state storage 213 that stores a value indicating a state ofthe input restriction.

The temperature detector 201 measures a temperature of at least oneplace in the input unit 200 at a determined timing, for example, everyfive minutes. The temperature detector 201 determines whether themeasured temperature exceeds a threshold stored in the threshold storage211, and when determination is made that the measurement value exceedsthe threshold stored in the threshold storage 211, sends to the CPU unit100 via the shared bus 410 a signal for notification of thedetermination result. The temperature detector 201 updates a parameterof the input setting 212 in accordance with the notification from theCPU unit 100. The temperature detector 201 is implemented by use of thetemperature measurement circuit 230 and the MPU 250. The temperaturedetector 201 is an example of determination means, acquisition means,and notification means of the present disclosure.

The input controller 202 switches between passage/blockage of the inputsignal from the detector 901 in accordance with content of the settingin the input setting 212. The input controller 202 is implemented by useof the input circuit 240 and the MPU 250.

The threshold storage 211 is a reference value indicating whether tonotify the CPU unit 100 of a temperature in the unit. The thresholdstorage 211 is an example of threshold storage means of the presentdisclosure.

The input setting 212 stores, for each input point, a parameterindicating whether the input signal is to be passed or blocked. Theinput setting 212 is updated upon issuance from the CPU unit 100 of aninstruction of input/output restriction or an instruction to cancel theinput/output restriction. The input setting 212 is implemented by thememory 210. The memory 210 is assumed to store a default value of theinput setting 212 when the input/output restriction is not in progress.

For example, when the input setting 212 for a certain input point is setON, the input controller 202 turns on the switching element for input ofthe input circuit 240 that is connected to the input point, and thusreceives the input signal from the detector 901. When the input setting212 for a certain input point is set to OFF, the input controller 202turns off the switching element of input of the input circuit 240 thatis connected to the input point, and thus blocks the input signal fromthe detector 901.

Values indicating the state of whether or not input/output restrictionis in progress for the input unit 200 are set in the restriction statestorage 213. In the restriction state storage 213, the value “1” is setas a value indicating that the input/output is in “restriction” or thevalue “0” is set as a value indicating that the input/output is in“non-restriction”. The threshold storage 211, the input setting 212, andthe restriction state storage 213 are implemented by use of the memory210.

The output unit 300 functionally includes a temperature detector 301that detects a temperature in the unit, an output controller 302 thatcontrols output to the control target device 902, a threshold storage311 that stores a threshold of a temperature that is a reference as towhether or not an output restriction is performed, an output setting 312that stores content of a setting with respect to passage/blockage of asignal at each output point, and a restriction state storage 313 thatstores a value indicating a state of the output restriction.

The temperature detector 301 measures a temperature of at least oneplace in the output unit 300 at a determining timing. The temperaturedetector 301 determines whether or not the measured temperature exceedsa threshold stored in the threshold storage 311, and when determinationis made that the measurement value exceeds the threshold stored in thethreshold storage 311, sends to the CPU unit 100 via the shared bus 410a signal for notification of the determination result. The temperaturedetector 301 updates a parameter of the output setting 312 in accordancewith the notification from the CPU unit 100. The temperature detector301 is implemented by using the temperature measurement circuit 330 andthe MPU 350. The temperature detector 301 is an example of thedetermination means, the acquisition means, and the notification meansof the present disclosure.

The output controller 302 switches between passage/blockage of theoutput signal to the control target device 902 in accordance withcontent of the setting in the output setting 312. The output controller302 is implemented by using the output circuit 340 and the MPU 350.

The threshold storage 311 is a reference value indicating whether tonotify the CPU unit 100 of a temperature in the unit. The thresholdstorage 311 is an example of the threshold storage means of the presentdisclosure.

The output setting 312 stores a parameter indicating, for each outputpoint, whether the output signal is to be passed or blocked. The outputsetting 312 is updated upon issuance, from the CPU unit 100 for eachoutput point, of an instruction for input/output restriction or aninstruction for unlocking of the input/output restriction. The outputsetting 312 is implemented by using the memory 310. The memory 310 isassumed to store a default value of the output setting 312 when theinput/output restriction is not in progress.

For example, when an output point is set to ON in the output setting312, the output controller 302 turns on the switching element for outputof the output circuit 340 connected to that output point and outputs theoutput signal to the control target device 902. When the output setting312 is set OFF for an output point, the output controller 302 turns offthe switching element for output of the output circuit 340 that isconnected to the output point, thereby blocking the output signal to thecontrol target device 902.

Values indicating whether or not the input/output restriction is on areset in the restriction state storage 313. In the restriction statestorage 313, the value “1” is set as a value indicating that theinput/output is in “restriction” or the value “0” is set as a valueindicating that the input/output is in “non-restriction”. The thresholdstorage 311, the output setting 312, and the restriction state storage313 are implemented by using the memory 310.

Next, a method for using the engineering tool 500 to set content ofrestriction with respect to the input/output is described. The userstarts the setting application 512 by operating the inputter 520, suchas a keyboard, a mouse, or the like. The CPU 550 executes the settingapplication 512 in response to a user's operation to achieve thefollowing functions.

First, the CPU 550 retrieves data relating to the configuration of theprogrammable logic controller 1 stored in the storage 510, and displayson the display 530 a screen indicating the configuration of the units ofthe programmable logic controller 1 as illustrated in FIG. 4A. The userselects, on the displayed screen as illustrated in FIG. 4A, the inputunit 200 or the output unit 300 for which setting with respect to theinput/output restriction is to be made, by operation of the inputter520. For example, the user is assumed to select an “input unit 1”. TheCPU 550 retrieves from the storage 510 the data relating to theinput/output point of the selected “input unit 1” in response to theuser's operation so as to display the screen as illustrated in FIG. 4Bon the display 530. Here, a screen for setting an operation during aninput/output restriction for each input point of the “input unit 1” isdisplayed on the display 530. The user operates the input device of theinputter 520 to select an input point. For example, the user is assumedto select an “input point 2” enclosed by a dashed line. The CPU 550retrieves the current set value from the restriction table 111 for theselected “input point 2” in response to the user's operation, anddisplays the screen as illustrated in FIG. 4C on the display 530. Here,a screen for setting of the input/output restriction of the “input point2” of the “input unit 1” is displayed on the screen. The user operatesthe input device of the inputter 520 to select an operation. Forexample, the user is assumed to select “STOP”. The CPU 550 responds tothe user's operation and turns on or off the value of the operation thatoccurs during the input/output restriction of the restriction table 111illustrated in FIG. 3.

Next, a sequential process flow relating to an input/output restrictionperformed cooperatively by the CPU unit 100, the input unit 200, and theoutput unit 300 is described. Before the start of the following process,the restriction state storage 112 of the CPU unit 100, the restrictionstate storage 213 of the input unit 200, and the restriction statestorage 313 of the output unit 300 are assumed to be set to the value“0” indicating the “non-restriction” state.

As illustrated in FIG. 5, upon arrival of the time of temperaturemeasurement (Yes in step S11), the temperature detector 201 of the inputunit 200 measures a temperature (step S12) and stores the measurementvalue in the memory 210. When the value “0” indicating the“non-restriction” state is set to the restriction state storage 213, thetemperature detector 201 determines that the state of non-restriction isin progress (Yes in step S13) and determines whether the measurementvalue exceeds a threshold of the threshold storage 211 (step S14). Whendetermination is made that the measurement value exceeds the thresholdof the threshold storage 211 (Yes in step S14), the temperature detector201 sends to the CPU unit 100 notification relating to a monitoringtemperature (step S15). Here, the temperature detector 201 may sendnotification that the measurement value exceeds the threshold of thethreshold storage 211. The output unit 300 also performs the processillustrated in FIG. 5, similarly to the input unit 200. By contrast,when determination is made that the measurement value does not exceedthe threshold of the threshold storage 211 (No in step S14), thetemperature detector 201 performs processing of step S11 again withoutsending to the CPU unit 100 the notification relating to the monitoringtemperature.

As illustrated in FIG. 6A, upon receiving from at least one of the inputunit 200 or the output unit 300 the notification relating to themonitoring temperature (Yes in step S21), the input/output manager 101of the CPU unit 100 determines, based on the value set to therestriction state storage 112, whether or not the non-restriction stateis in progress (step S22). When the value “0” indicating the“non-restriction” state is set to the restriction state storage 112 (Yesin step S22), the input/output manager 101 retrieves content ofrestriction relating to the input/output from the restriction table 111(step S23). For example, upon receipt of the notification relating tothe monitoring temperature from the input unit 200, the input/outputmanager 101 retrieves, from the restriction table 111 for all the inputpoints of the input units 200 that are to be target units, settingvalues of ON/OFF that occur during the input/output restriction. Here,the restriction state storage 112 is off, that is, the input/outputrestriction is not in progress for the input unit 200 or the output unit300 that sends the notification relating to the monitoring temperature.This is because the notification relating to the monitoring temperatureis sent from the input unit 200 or the output unit 300 since thetemperature in the unit exceeds the threshold, and the unit having sentthe notification relating to the monitoring temperature is to besubjected to the input/output restriction.

The input/output manager 101 updates the value of the restriction statestorage 112 with the value “1” indicating that the “restriction” stateis in progress (step S24), and sends an instruction to perform aninput/output restriction to the transmission source of the notificationrelating to the monitoring temperature (step S25). At this time, theinput/output manager 101 notifies the source of the notificationrelating to the monitoring temperature, about a parameter specifyingON/OFF of each input/output point during the input/output restrictionand retrieved from the restriction table 111 in step S23. For example,when the notification relating to the monitoring temperature is receivedfrom the input unit 200, the input/output manager 101 sends to the inputunit 200 a parameter relating to the input/output restriction havingcontent of “input point1: OFF, input point 2: OFF, input point 3: OFF,input point 4: OFF, . . . , input point 15: ON, input point 16: OFF”.

As illustrated in FIG. 6B, upon receiving an instruction for theinput/output restriction from the CPU unit 100 (Yes in step S31), thetemperature detector 201 of the input unit 200 updates the value of theinput setting 212 with a parameter relating to the input/outputrestriction received from the CPU unit 100 (step S32). Thereafter, theinput controller 202 turns on or off the switching element for input ofthe input circuit 240 in accordance with the updated input setting 212.In addition, the temperature detector 201 sets the restriction statestorage 213 to the value “1” indicating that the “restriction” state isin progress (step s33). The output unit 300 is assumed to perform aprocess illustrated in FIG. 6B, similarly to the input unit 200.

The input/output restriction is assumed to decrease a temperature in theunit that is the input unit 200 or the output unit 300. In this case,the CPU unit 100, the input unit 200, and the output unit 300 perform aprocess to cancel the input/output restriction. Before the start of thefollowing process, the restriction state storage 112 of the CPU unit100, the restriction state storage 213 of the input unit 200, and therestriction state storage 313 of the output unit 300 are assumed to beset to the value “0” indicating the “restriction” state.

As illustrated in FIG. 5, upon arrival of the time of temperaturemeasurement (Yes in step S11), the temperature detector 201 of the inputunit 200 measures a temperature (step S12) and stores the measurementvalue in the memory 210. The temperature detector 201 determines, basedon the value set to the restriction state storage 213, whether the“non-restriction” state is in progress (step S13). When the value “1”indicating that the restriction state is in progress is set to therestriction state storage 213, the temperature detector 201 determinesthat the non-restriction state is in progress, that is, determines thatthe restriction state is in progress (No in step S13), and determineswhether the measurement value is equal to or less than the threshold ofthe threshold storage 211 (step S16). When determination is made thatthe measurement value is equal to or less than the threshold of thethreshold storage 211 (Yes in step S16), the temperature detector 201sends to the CPU unit 100 the notification relating to the monitoringtemperature (step S17). Here, the temperature detector 201 may sendnotification that the measurement value is equal to or less than thethreshold of the threshold storage 211. The output unit 300 is assumedto perform a process illustrated in FIG. 5, similarly to the input unit200. By contrast, when determination is made that the measurement valueexceeds the threshold of the threshold storage 211 (No in step S16), thetemperature detector 201 performs processing of step S11 again withoutsending to the CPU unit 100 the notification relating to the monitoringtemperature.

As illustrated in FIG. 6A, upon receiving from at least one of the inputunit 200 or the output unit 300 the notification relating to themonitoring temperature (Yes in step S21), the input/output manager 101of the CPU unit 100 determines, based on the value set to therestriction state storage 112, whether or not the non-restriction stateis in progress (step S22). When the value “1” indicating the restrictionstate is set in the restriction state storage 112, the input/outputmanager 101 determines that the restriction is in progress (No in stepS22), and sets in the restriction state storage 112 the value “0”indicating the “non-restriction” state (step S26). Here, at the time ofreception of the notification relating to the monitoring temperature,the value “1” is set in the restriction state storage 112. That is, theinput/output is restricted in the input unit 200 or the output unit 300to which the notification relating to the monitoring temperature issent. This is because the notification relating to the monitoringtemperature is sent from the input unit 200 or the output unit 300 sincethe temperature in the unit is equal to or less than the threshold, andthe unit having sent the notification relating to the monitoringtemperature is to be subjected to the input/output restriction.

The input/output manager 101 sends an instruction to cancel theinput/output restriction to the source of the notification relating tothe monitoring temperature (step S27).

As illustrated in FIG. 6B, upon not receiving the notification of theinput/output restriction (No in step S31) and receiving the notificationto cancel the input/output restriction (Yes in step S34) from the CPUunit 100, the temperature detector 201 of the input unit 200 updates thevalue of the input setting 212 with a default value stored in the memory210 (step S35). Thereafter, the input controller 202 turns on or off theswitching element for input of the input circuit 240 in accordance withthe updated input setting 212. In addition, the input controller 202sets the restriction state storage 213 to the value indicating a“non-restriction” state (step S36). The output unit 300 is assumed toperform a process illustrated in FIG. 6B, similarly to the input unit200.

As described above, when the temperature in the unit of the input unit200 or the output unit 300 exceeds the threshold, the programmable logiccontroller 1 according to the embodiment does not restrict theinput/output for the input/output point specified in the unit.

Such configuration can achieve a continuous operation for theinput/output that is not to be restricted, while preventing failure ofthe input unit 200 and the output unit 300. For example, an input signalfrom an emergency stop of a device or an input signal from an aircurtain can be set so that supply of the input signal to the CPU unit100 is not stopped. Furthermore, the temperature in the unit ismonitored, and when the temperature in the unit is equal to or less thanthe threshold, the input/output restriction is canceled. Thuscontinuation of unnecessary input/output restriction can be prevented.

Modified Example 1

In the embodiment, the input/output manager 101 performs control to turnoff all the input/output points set to be OFF in the restriction table111. But the present disclosure is not limited to such a configuration.For example, the input/output manager 101 may control the input/outputpoint that is set OFF to have a shortened output period. In the exampleillustrated in FIG. 7A for the output point 3, although the input/outputmanger 101 prior to restriction continuously outputs an output signalduring a period represented by dashed lines. During restriction, theinput/output manager 101 does not output an output signal during aperiod represented by dashed lines and outputs the output signal onlyduring the period represented by a solid line. Such operation shortensthe period for output of the output signal.

Alternatively, the input/output manager 101 may control the input/outputnumber of times of the input/output point set to be OFF to be decreased.In the example illustrated in FIG. 7B, before the restriction, theinput/output manger 101 continuously outputs an output signalrepresented by dashed lines for the output point 2. However, duringrestriction, the input/output manager 101 does not output an outputsignal represented by dashed lines and outputs only the output signalrepresented by dashed lines. In this way, the number of times ofoutputting the output signal decreases.

Modified Example 2

In the above embodiment, each input/output point in the restrictiontable 111 is set ON or OFF during the input/output restriction and theinput/output manager 101 turns off all the input/output points set OFFin the restriction table 111. However, there is a case where thespecified input/output points do not have to be OFF, depending on adegree of an increase in temperature in the unit. Thus the input/outputmanager 101 may control ON/OFF of the input/output points as follows.

FIG. 8 illustrates an example of data registered in a restriction table111 a according to Modified Example 2. The restriction table 111 aincludes setting of a priority level indicating an order of priority foreach of the input/output points. Here, any one of the values “level 1”,“level 2”, and “level 3” is set as the priority level. The “level 3”indicates the input/output point that is restricted first during theinput/output restriction. The “level 2” indicates the input/output pointfor which restriction comes next after a level 3 during the input/outputrestriction. The “level 1” indicates the input/output point that is notrestricted, that is, not turned off during the input/output restriction.In Modified Example 2, the order of setting OFF increases with magnitudeof the level value.

In Modified Example 2, two thresholds are set that indicating areference as to whether restriction is performed based on the measuredtemperature. The reference temperature for restriction of the level 3input/output points is set as a first threshold. The referencetemperature for restriction of the level 2 input/output points is set asa second threshold. The temperature specified as a second threshold ishigher than the temperature specified as the first threshold.

In this case, as illustrated in FIG. 9, upon arrival of the time oftemperature measurement (Yes in step S41), the temperature detector 201of the input unit 200 measures a temperature (step S42), and determineswhether the measurement value exceeds the second first threshold or thesecond threshold (step S43). When determination is made that themeasurement value exceeds the first threshold or the second threshold(Yes in step S43), the temperature detector 201 notifies the CPU unit100 that the measurement value exceeds the first threshold or the secondthreshold (step S44). By contrast, the temperature detector 201 performsprocessing step S41 again when determination is made that themeasurement value does not exceed the first threshold or the secondthreshold (No in step S43).

By contrast, when determination is made that the measurement value doesnot exceed the first threshold or the second threshold in step S43 (Noin step S43), the temperature detector 201 performs processing of stepS41 again. The output unit 300 also performs processing of the flowillustrated in FIG. 9, similarly to the input unit 200.

As illustrated in FIG. 10, when determination is made that themeasurement value of the temperature in the unit exceeds the firstthreshold or the measurement value of the temperature in the unitexceeds the second threshold based on the notification relating to thereceived monitoring temperature from at least one of the input unit 200or the output unit 300 (Yes in step S51), the input/output manager 101of the CPU unit 100 retrieves content of restriction relating to theinput/output from the restriction table 111 a (step S52). For example,upon receiving the notification relating to the monitoring temperaturefrom the input unit 200, the input/output manager 101 retrieves, fromthe restriction table 111 a, setting values of ON/OFF during theinput/output restriction for all the input points of the input units 200serving as the target units.

The input/output manager 101 determines, based on the notification fromthe input unit 200 or the output unit 300, whether the measurement valueexceeds the second threshold (step S53). When determination is made thatthe measurement value exceeds the second threshold (Yes in step S53),the input/output manager 101 notifies the source of the measurementvalue to restrict the input/output points with priority levels set to“level 2” and “level 3” in the restriction table 111 a illustrated inFIG. 8 (step S54). By contrast, as illustrated in FIG. 10, whendetermination is made the measurement value does not exceed the secondthreshold, that is, the measurement value exceeds the first threshold instep S53 (No in step S53), the input/output manager 101 notifies thesource of the measurement value to restrict the input/output points withthe priority levels set to “level 3” in the restriction table 111 aillustrated in FIG. 8 (step S55). This is because in this case themeasurement value does not exceed the second threshold but exceeds thefirst threshold.

As described above, in Modified Example 2, the input/output restrictioncan be performed stepwise in accordance with a degree of an increase intemperature in the unit.

Modified Example 3

In the embodiment and Modified Examples 1 and 2, the examples in which auser sets ON/OFF, priority levels and the like for all the input/outputpoints are described. However, in a case where there are too manyinput/output points, setting ON/OFF, priority levels, and the like inthe restriction table 111 for all the input/output points by the user issometimes difficult.

In Modified Example 3, the CPU unit 100 automatically selects aninput/output point for turning OFF. The user needs to previously set inthe restriction table 111 an input/output point for which a continuousoperation is needed, that is, an input/output point that is not to beturned OFF, using the engineering tool 500 similarly to the embodiment.

A method for setting a parameter of the restriction table 111 by the CPUunit 100 is described below. The input unit 200 is assumed to send, atcertain time intervals, data indicating a history of the input periodand a number of times of occurrence of the input signal to the CPU unit100. The same applies to the output unit 300.

As illustrated in FIG. 11, upon receiving from at least one of the inputunit 200 or the output unit 300 data relating to a history of theinput/output signals in the input unit 200 or the output unit 300 (Yesin step S61), the input/output manager 101 of the CPU unit 100 registersthe received data as a log (step S62).

The input/output manager 101 determines the content of restriction basedon the log and the restriction table 111 (step S63). Specifically, theinput/output manager 101 retrieves the content of restriction relatingto the input/output from the restriction table 111. As described above,in Modified Example 3, the input/output point that is to be continuouslyON during the input/output restriction is specified in the restrictiontable 111. Thus the input/output manager 101 determines from the log atotal amount of time obtained by a sum of lengths of the input/outputtime in a certain period of time, for each of the input/output pointsother than the input points previously set by a user to the restrictiontable 111 so as to continuously be ON, and restricts as a restrictiontarget the input/output points whose total amount of time exceeds areference value. The input/output manager 101 updates the restrictiontable 111 with the determined content of restriction.

Such a configuration enables automatic setting of the content of theinput/output restriction for the input/output point specified by theuser without turning the input/output point OFF. This can preventfailure of the input unit 200 and the output unit 300. Thus theinput/output that is not to be restricted can achieve continuousoperation while failure of the input/output unit is prevented.

Alternatively, the input/output manager 101 may select as a restrictiontarget the N input points (N is an integer) of the input points havingthe greatest total amounts of time.

Modified Example 4

In the embodiment and Modified Examples 1 to 3, determination as towhether or not the temperature in the input unit 200 exceeds thethreshold of the threshold storage 211 is made in the input unit 200 anddetermination as to whether the temperature in the output unit 300exceeds the threshold of the threshold storage 311 is made in the outputunit 300, but the present disclosure is not limited to suchconfiguration. The input unit 200 and the output unit 300 may simplysend the measurement value of the temperature in the unit to the CPUunit 100.

In this case, the threshold of the input unit 200 and the threshold ofthe output unit 300 are previously stored in the memory 110 of the CPUunit 100. Determination by the input/output manager 101 of the CPU unit100 as to whether the measurement value received from the input unit 200exceeds the threshold of the input unit 200 is sufficient. Whendetermination is made that the temperature in the input unit exceeds thethreshold of the input unit, the input/output manager 101 instructs theinput unit 200 to perform an input/output restriction. The same appliesto the output unit 300. In this case, the input/output manager 101 is anexample of determination means of the present disclosure.

For cancellation of the input/output restriction, in the embodiment andModified Examples 1 to 3, determination as to that the temperature inthe input unit 200 is equal to or less than the threshold of thethreshold storage 211 is made in the input unit 200, and determinationas to whether the temperature in the output unit 300 is equal to or lessthan the threshold of the threshold storage 311 is made in the outputunit 300, but the present disclosure is not limited to suchconfiguration. The input unit 200 and the output unit 300 may simplysend the measurement value of the temperature in the unit to the CPUunit 100.

Determination by the input/output manager 101 of the CPU unit 100 as towhether the temperature in the input unit 200 is equal to or less thanthe threshold of the input unit 200 is sufficient. When determination ismade that the temperature in the input unit 200 is equal to or less thanthe threshold of the input unit 200, the input/output manager 101instructs the input unit 200 to cancel the input/output restriction. Thesame applies to the output unit 300.

The embodiment and Modified Examples 1 to 4 describe an example ofperforming the input/output restriction of the input unit 200 and theoutput unit 300 that are function units different from the CPU unit 100,but the present invention is not limited to such configuration. Forexample, the CPU unit 100 itself may have at least one function of theinput function or the output function. In this case, the CPU unit 100may control passage/blockage of a signal supplied from the detector 901connected to the CPU unit 100 and a signal to be supplied to the controltarget device 902.

Alternatively, the input unit 200 itself that is a function unit mayperform an input restriction. Specifically, the input unit 200 isdesigned to include a restriction table 111, and the input unit 200performs control of passage/blockage of the signal supplied from thedetector 901 in accordance with the control content set in therestriction table 111 based on the measured temperature. Similarly, theoutput unit 300 itself may perform the output restriction.

In the above embodiment, an example of monitoring the temperatures inthe units that are the input unit 200 and the output unit 300 isdescribed, but the present disclosure is not limited to suchconfiguration. For example, a temperature sensor may be mounted on anenclosure of the unit, and the input/output restriction may be performedbased on the measurement value of the temperature sensor. Alternatively,a temperature sensor may be provided near the unit, and the input/outputrestriction may be performed based on the temperature around the unit.

As a recording medium for recording the above programs, a universalserial bus (USB) memory, a flexible disc, a compact disc (CD), a digitalversatile disc (DVD), Blu-ray (registered trademark), a magneto-opticaldisc (MO), a secure digital (SD) card, Memory Stick (registeredtrademark), or a computer-readable recording medium including a magneticdisk, an optical disk, a magneto-optical disk, a semiconductor memory,and a magnetic tape can be used.

The foregoing describes some example embodiments for explanatorypurposes. Although the foregoing discussion has presented specificembodiments, persons skilled in the art will recognize that changes maybe made in form and detail without departing from the broader spirit andscope of the invention. Accordingly, the specification and drawings areto be regarded in an illustrative rather than a restrictive sense. Thisdetailed description, therefore, is not to be taken in a limiting sense,and the scope of the invention is defined only by the included claims,along with the full range of equivalents to which such claims areentitled.

REFERENCE SIGNS LIST

-   1 Programmable logic controller-   100 CPU unit-   210, 310, 510 Storage-   101 Input/output manager-   110, 210, 310 Memory-   111, 111 a Restriction table-   112, 213, 313 Restriction state storage-   120, 220, 320 Input/output I/F circuit-   130 Tool I/F circuit-   140, 550 CPU-   190, 290, 390, 590 Bus-   200 Inputter-   201, 301 Temperature detector-   202 Input controller-   211, 311 Threshold storage-   212 Input setting-   230, 330 Temperature measurement circuit-   240 Input circuit-   250, 350 MPU-   300 Output unit-   302 Output controller-   340 Output circuit-   310 Storage device-   312 Output setting-   400 Base unit-   410 Shared bus-   500 Engineering tool-   501 Communication cable-   511 Operating system program-   512 Setting application-   520 Inputter-   530 Display-   540 Tool interface-   901 Detector-   902 Control target device-   1001, 1002 Input point

The invention claimed is:
 1. A programmable logic controller comprising:circuitry configured to implement a central processing unit (CPU) unit;a function unit having at least one of an input function of inputting tothe CPU unit a signal supplied from an external device or an outputfunction of outputting to the external device a signal supplied from theCPU unit; an acquirer to acquire a temperature of the function unit; acontroller to control, when the temperature of the function unitsatisfies a preset condition, passage and blockage of the signal fromthe external device to the function unit or the signal from the functionunit to the external device, in accordance with preset content of signalinput/output restriction; and a restriction storage to store, for eachsource of the signal as the content of the restriction, informationindicating whether or not restriction to shorten a period of time topass the signal is imposed when the temperature of the function unit ishigher than a specified threshold, wherein when the temperature of thefunction unit is higher than the threshold, the controller shortens timeto pass the signal specified in the restriction storage to be shorterthan that when the temperature of the function unit is not higher thanthe threshold.
 2. The programmable logic controller according to claim1, wherein when the temperature of the function unit is equal to orlower than the threshold after exceeding the threshold, the controllerextends time to pass the signal specified in the restriction storage tobe longer than that when the temperature of the function unit is higherthan the threshold.
 3. The programmable logic controller according toclaim 1, wherein when the temperature of the function unit is higherthan the threshold, the controller increases the number of times ofblocking the signal specified in the restriction storage so as to bemore than that when the temperature of the function unit is not higherthan the threshold.
 4. The programmable logic controller according toclaim 3, wherein when the temperature of the function unit is equal toor lower than the threshold after exceeding the threshold, thecontroller increases the number of times of passing the signal specifiedin the restriction storage so as to be more than that when thetemperature of the function unit is higher than the threshold.
 5. Theprogrammable logic controller according to claim , wherein therestriction storage further stores a signal blocking order for eachsignal, and when the temperature of the function unit is higher than thethreshold, the controller blocks the signal sequentially in accordancewith the signal blocking order stored in the restriction storage.
 6. Theprogrammable logic controller according to claim 1, wherein when aperiod that is a total amount of periods of signal supply from theexternal device to the function unit is longer than a reference value ina certain period, the controller extends time to block the signal to belonger than that when the total amount of periods is not longer than thereference value.
 7. The programmable logic controller according to claim1, wherein the circuitry is configured to implement the function unitsuch that the function unit comprises a threshold storage to store thethreshold, a determiner to determine whether the temperature in thefunction unit is higher than a preset threshold, and a notifier tonotify the CPU unit that the temperature in the function unit is higherthan the threshold.
 8. The programmable logic controller according toclaim 1, wherein the circuitry is configured to implement the functionunit such that the function unit comprises a notifier to notify the CPUunit of the temperature inside the function unit, and the CPU unitcomprises a threshold storage to store the threshold, and a determinerto determine whether the temperature inside the function unit is higherthan a preset threshold.
 9. A central processing unit (CPU) unit havingat least one of an input function of receiving a signal supplied from anexternal device or an output function of outputting a signal to theexternal device, the CPU unit comprising: circuitry configured toimplement an acquirer to acquire a temperature of the CPU unit; acontroller to control, when the temperature of the CPU unit satisfies apreset condition, passage and blockage of the signal in accordance withpreset content of restriction for each of input/output points; and arestriction storage to store, for each source of the signal as thecontent of the restriction, information indicating whether or notrestriction to shorten a period of time to pass the signal is imposedwhen the temperature of the CPU unit is higher than a specifiedthreshold, wherein when the temperature of the CPU unit is higher thanthe threshold, the controller shortens a period of time to pass thesignal specified in the restriction storage to he shorter than that ofwhen the temperature of the CPU unit is not higher than the threshold.10. A function unit, comprising circuitry configured to implement thefunction unit having an input function of inputting to a centralprocessing unit (CPU) unit a signal supplied from an external device andan output function of outputting to the external device a signalsupplied from the CPU unit, the circuitry being configured such that thefunction unit comprises: an acquirer to acquire a temperature of thefunction unit; a controller to control, when the temperature of thefunction unit satisfies a preset condition, passage and blockage of thesignal in accordance with preset content of restriction for each ofinput/output points; and a restriction storage to store, for each sourceof the signal as the content of the restriction, information indicatingwhether or not restriction to shorten a period of time to pass thesignal is imposed when the temperature of the function unit is higherthan a specified threshold, wherein when the temperature of the functionunit is higher than the threshold, the controller shortens a period oftime to pass the signal specified in the restriction storage to beshorter than that of when the temperature of the function unit is nothigher than the threshold.